1. Field of the Invention
The present invention relates to a plasma lighting system using electromagnetic wave, and more particularly, to a dielectric mirror for a plasma lighting system.
2. Description of the Background Art
Generally, an optical source for illumination is divided into an incandescent lamp using heat radiation, a fluorescent lamp using a fluorescent body at a discharge pipe, a high intensity discharge lamp (HID lamp) using luminance by a discharge of gas of a high pressure or vapor, and a plasma lighting system using an electrodeless discharge.
The incandescent lamp has a high color rendering, a small size, a simple lighting circuit, and a low price. However, the incandescent lamp has a low optical efficiency and a short life span. The fluorescent lamp has an optical efficiency higher than that of the incandescent lamp and a life span longer than that of the incandescent lamp. However, the fluorescent lamp has a relatively large size and requires an additional lighting circuit. The HID lamp has a high optical efficiency and a long life span. However, the HID lamp requires time in lighting and re-lighting and needs an additional lighting circuit. The PLS lamp has a life span longer than any other lamp and a highest optical efficiency. However, the PLS lamp has a large consumption power and a high price, and requires an additional lighting circuit.
The PLS lamp is recognized as a new optical source. A plasma lighting system using the PLS lamp emits light of a high optical amount without an electrode by making a discharge material inside a bulb into plasma by electromagnetic wave generated from a magnetron of a microwave oven and thereby continuously emitting light by a metal compound.
The bulb of the plasma lighting system contains a main discharge material such as a metal, a halogen-based compound, sulfur, or selenium for emitting light by forming a plasma, an initial discharge material such as Ar, Xe, Kr, etc. for forming plasma inside a light emitting portion at the time of an initial luminance, and a discharge catalyst material such as Hg for facilitating lighting by an initial discharge or controlling a light spectrum.
FIG. 1 is a longitudinal section view showing one example of a plasma lighting system in accordance with the conventional art, and FIG. 2 is a perspective view showing a dielectric mirror in the plasma lighting system in accordance with the conventional art.
As shown, the conventional plasma lighting system comprises a magnetron 20 mounted in a casing 10 and generating electromagnetic wave, a high voltage generator 30 for supplying alternating current (AC) power to the magnetron 20 by boosting into a high voltage, a wave guide 40 connected to an outlet of the magnetron 20 for transmitting electromagnetic wave generated from the magnetron 20, a resonator 50 connected to an outlet of the wave guide 40 for resonating the electromagnetic wave passing through the wave guide 40, a bulb 60 disposed in the resonator 50 for emitting light by making the discharge materials filled therein into plasma by electromagnetic wave, a reflector 70 containing the resonator 50 therein for forwardly reflecting light generated from the bulb 60, a dielectric mirror 80 mounted in the resonator 50 positioned at a rear side of the bulb 60 for passing electromagnetic wave and reflecting light, and an electromagnetic wave guiding plate 90 covering the outlet of the wave guide 40 and having an electromagnetic wave passing hole 91 for connecting the wave guide 40 and the resonator 50 to each other.
The bulb 60 comprises a light emitting portion 61 having an inner volume and a sphere shape formed of a quartz material, disposed outside the casing 10, and having a discharge material, a discharge catalyst material, etc. therein for emitting light by making the inner materials into plasma; and a supporting portion 62 integrally extending from the light emitting portion 61 and supported in the casing 10.
As shown in FIG. 2, the dielectric mirror 80 comprises a glass plate 81 formed of a quartz material so as to be endurable against a high temperature, and a reflection coating layer 82 coated at one side of the glass plate 81 for reflecting light generated from the bulb 60 in a forward direction.
The electromagnetic wave guiding plate 90 is provided with the electromagnetic wave passing hole 91 for guiding electromagnetic wave to the resonator 50 by connecting the wave guide 40 and the resonator 50 to each other at the center thereof. Also, a fixing portion 92 having the electromagnetic wave passing hole 91 for fixing the reflector 70 at an outer circumferential surface thereof and fixing the dielectric mirror 80 thereon is formed at one side of the electromagnetic wave guiding plate 90. The fixing protrusion 92 has a height not to cover the light emitting portion 61 of the bulb 60.
An unexplained reference numeral 11 denotes an air inlet, 12 denotes an air outlet, 13 denotes an air flow path, F denotes a cooling fan, M1 denotes a bulb motor for rotating the bulb, and M2 denotes a fan motor for rotating the cooling fan.
An operation of the conventional plasma lighting system will be explained as follows.
When a driving signal is inputted to the high voltage generator 30 by a controller, the high voltage generator 30 boosts alternating current (AC) power thus to supply it to the magnetron 20. Then, the magnetron 20 is oscillated by the high voltage thus to generate electromagnetic wave having a high frequency. The electromagnetic wave is emitted into the resonator 50 through the wave guide 40, and continuously excites the discharge material and the discharge catalyst material contained in the bulb 60 into a plasma state. As the result, light having a specific emission spectrum is generated, and the light is forwardly reflected by the reflector 70 and the dielectric mirror 80 thus to illuminate a space.
However, the conventional plasma lighting system has the following problem. When the reflection coating layer 82 is formed at the glass plate 81 formed of a quartz material in order to fabricate the dielectric mirror 80, the reflection coating layer 82 is degraded by heat of a high temperature thus to be damaged. As the result, when the reflection coating layer 82 is used for a long time, a reflection efficiency is lowered.